Lithium halide flux for treating magnesium-lithium alloys



United States Patent LITHIUM HALIDE FLUX FOR TREATING MAGNESIUM-LITHIUMALLOYS Paul D. Frost, Columbus, Ohio, assignor, by mesneassignments, toOlin Mathieson Chemical Corporation, a corporation of Virginia NoDrawing. Application June 30, 1948, Serial N0. 36,292

1 Claim. (CI. 75-67) This invention relates to fluxes for the treatmentof magnesium alloys and provides an improved flux for use in meltingmagnesium-lithium base alloys, especially those containing appreciableamounts of heavy alloying elements.

A melting flux effectively used for magnesium-lithium base alloys hasbeen described in a patent application of Alfred H. Hesse, entitledFluxes, Serial No. 603,749, filed July 7, 1945, now Patent No. 2,507,713and cornprises from 60% to 98% of a chloride component and from 40% to2% of a fluoride component, said chloride component consisting of from 0to 50% of potassium chloride, from 0 to of alkaline earth metal chlorideand the balance lithium chloride and said fluoride component consistingof at least one fluoride of the group consisting of potassium fluoride,lithium fluoride and alkaline earth metal fluoride, the total of thealkaline earth metal chloride and fluoride being less than of the flux,said flux as initially used being practically free of sodium. This fluxis especially useful with alloys whose specific gravity in the solidstate is around 1.5 and is satisfactory for nearly all Mg-Li alloys.Ordinarily, the LiCl-LiF flux, being heavier than the Mg-Li alloys,remains for the most part below the melt with a thin film of fluxcovering the top of the melt and protecting it from reactive gases.However, certain recently developed high-strength alloys contain heavyalloying elements and have specific gravities of the order of 1.66 to1.70, and in melting some of these heavier alloys, it has been founddifficult to obtain good separation of the flux from the metal duringpouring. Therefore, it is desirable in some cases to increase thespecific gravity of the flux. This has been done recently by addingBaClz to the flux before pouring. However, it has now been found thatBaClz is undesirable because it is likely to break down and contaminatethe Mg-Li alloys with metallic barium.

I have confirmed my conception that LiBr is an effective addition saltto increase the specific gravity of the LiCl-LiF flux. In accordancewith my invention, I substitute LiBr for a major part of the LiCl andthe LiF of the fluxes of the type described in said application.Previous investigation had shown that a eutectic existed at aboutLiBr-25% LiCl and that this eutectic melted at about 970 F. It has nowbeen found that the melting point can be reduced to about 825 F. by theaddition of 10% LiF. The combination of around 3 parts LiBr, 1 partLiCl, plus about 10% LiF has been used as a melting flux with heats ofmagnesium-lithium base alloys and found to be extremely fluid (becauseof its low melting temperature) during the first part of the melt, butto thicken considerably before pouring. The experimental heats werecarried out with alloys comprising 6 Mg/Li, 16% Cd, 5% Ag. Thetheoretical density of the 3 LiBr/LiCl-10% LiF flux is about 2.93 g./cc.(solid) as against about 2.18 g./cc. for a 75 LiCl-25% LiF flux. Apreferred flux would have a density somewhere between the two values.

A flux consisting of 75% LiBr-25% LiCl has also I been tried andobserved to act in a manner similar to the LiBr-LiCl-LiF flux. Inseveral cases some burning was noted and it is believed that the densityof the flux had been increased too much by the inclusion of too great aproportion of LiBr. Experimental results definitely show that the meltedalloys can be poured or cast without difficulties caused by poorseparation between the flux and the alloy.

I claim:

A flux for the treatment of molten magnesium-lithium base alloysconsisting of about 3 parts LiBr, 1 part LiCl and about 10% LiF.

No references cited.

